Currently, during the fabrication process, the delicate and valuable substrates, including wafers for fabricating semiconductor devices, magnetic storage disc substrates, and LCD panel substrates, need to be transported continuously for various process steps. Nonetheless, these kinds of substrates are vulnerable to damages caused by environmental influences such as dust, electrostatic discharge, vibration, and gaseous containment.
Dust and the pollutants in the form of particles coming from the atmosphere will adhere to the substrates and cause irreversible damages. Because the size of integrated circuits is kept shrinking, the size of the particles threatening integrated circuits becomes smaller. Thereby, minimizing the pollutants has become extremely important. In the semiconductor industry, complicated methods, such as clean rooms, are adopted for preventing the environmental influences on the substrates.
As described above, it is required to protect substrate in each step of fabrication. Presently, a substrate cassette is used for accommodating substrate and isolating the substrates from the contact of external environment. Hence, damages on the substrate owing to the influences of the environment can be prevented. The substrate cassette described above includes, for example, the Front Opening Unified Pod system (FOUP). During the transit process of the substrate cassette, it can hold the substrates firmly. Nonetheless, the substrates tend to rub against the substrate cassette and generate particulate pollutants. Thereby, the material of current substrate cassette is an abrasion-resistive plastic material for preventing particulates generation between the substrates and the substrate cassette.
When substrates, including wafers or the substrates for semiconductor devices, are stored in the substrate cassette according to the prior art, vibration occurs and a substantial amount of static charges are generated due to the friction between the substrates and the substrate cassette. The static charges will be remained on the substrates. As the substrates are removed from the substrate cassette, ESD damages occur in the removed substrates because of the friction between the substrates and the substrate cassette. Thereby, it is required to eliminate the residual static charges on the substrates for avoiding electrostatic damages in the substrates.
Accordingly, the present invention provides an anti-electrostatic substrate cassette, which can discharge static charges for avoiding ESD in the substrates due to friction and thus improving the yield of the substrates.